Piezoelectric device liquid ejecting head, liquid ejecting apparatus, ultrasonic device sensor, and timing device

ABSTRACT

A liquid ejecting head comprises a pressure chamber communicating with nozzle and a piezoelectric actuator including a piezoelectric layer and an electrode which applies a voltage to the piezoelectric layer. The piezoelectric layer is composed of a solid solution containing bismuth sodium titanate and 0.2 mol % or more and 8.0 mol % or less of copper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2010-092906 filed Apr. 14, 2010, the contents of whichare hereby incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a liquid ejecting head, a liquidejecting apparatus, and a piezoelectric element.

2. Related Art

A liquid ejecting head is used as a component of a liquid ejectingapparatus such as an ink jet printer. In an ink jet printer, a liquidejecting head is configured to eject and fly droplets of ink such thatthe ink is made to adhere to media such as paper sheets. In this way,printing is performed with the ink jet printer.

In general, such a liquid ejecting head includes an actuator thatapplies pressure to liquid to thereby eject the liquid from nozzles ofthe liquid ejecting head. Such an actuator includes, for example, apiezoelectric element. For example, such a piezoelectric element in anactuator has a structure in which a piezoelectric layer composed of apiezoelectric material having an electromechanical transduction functionsuch as a crystallized piezoelectric ceramic is sandwiched between twoelectrodes. Such a piezoelectric element is configured to deform underthe application of a voltage by the two electrodes. Due to thedeformation of the piezoelectric element, the actuator can be operatedin, for example, a flexural vibration mode.

Piezoelectric materials used for such an application desirably have agood piezoelectricity such as electromechanical transduction efficiency.Accordingly, lead zirconate titanate (PZT) materials, which areexcellent in terms of the piezoelectricity compared with othermaterials, have been studied and developed. However, while there hasbeen an ever increasing demand for piezoelectric materials with enhancedpiezoelectricity and there has also been a demand for piezoelectricmaterials having a lower environmental load in recent years, it isdifficult to meet these demands with PZT materials. Thus, for example,perovskite-oxide piezoelectric materials, which have less lead content,have been developed.

The piezoelectricity of piezoelectric elements can be evaluated with theshape of a hysteresis loop obtained by subjecting the piezoelectricelements to a P-E measurement. Bismuth sodium titanate, which can berepresented by, for example, (Bi_(0.5), Na_(0.5))TiO₃ (hereafter,sometimes abbreviated as “BNT”), has been regarded as a promisingpiezoelectric material. However, although BNT in the form of a bulkexhibits a general hysteresis loop, in spite of the same BNTcomposition, BNT in the form of a thin film has a high leakage currentand does not exhibit a good hysteresis loop (For example, refer toJP-A-2005-105295).

SUMMARY

An advantage of some aspects of the invention is to provide a liquidejecting head including a piezoelectric layer having a low environmentalload and a good piezoelectricity; and a liquid ejecting apparatusincluding such a liquid ejecting head. Another advantage of some aspectsof the invention is to provide a piezoelectric element including apiezoelectric layer having a low environmental load and a goodpiezoelectricity.

The invention has been accomplished to achieve at least a part of theadvantages and can be embodied as the following aspects or embodiments.

First Embodiment

A liquid ejecting head according to a first aspect of the inventionincludes a piezoelectric actuator including a piezoelectric layer formedby a thin-film method and an electrode that applies a voltage to thepiezoelectric layer, wherein the piezoelectric layer is composed of asolid solution containing bismuth sodium titanate and 0.2 mol % or moreand 8.0 mol % or less of copper.

According to the liquid ejecting head of the first embodiment, althoughthe liquid ejecting head includes a piezoelectric layer containingbismuth sodium titanate having a low environmental load, thepiezoelectric layer can have a low leakage current and a goodpiezoelectricity.

Second Embodiment

In the first embodiment, the piezoelectric layer may contain 0.2 mol %or more and 4.0 mol % or less of copper.

According to the liquid ejecting head of the second embodiment, thepiezoelectric layer can have a lower leakage current and a betterpiezoelectricity.

Third Embodiment

In the first or second embodiment, the piezoelectric layer may furthercontain barium titanate.

According to the liquid ejecting head of the third embodiment, althoughthe piezoelectric layer further contains barium titanate, thepiezoelectric layer can have a low leakage current and a goodpiezoelectricity.

Fourth Embodiment

In the third embodiment, the piezoelectric layer may contain less than100 mol % and 85 mol % or more of the bismuth sodium titanate and morethan 0 mol % and 15 mol % or less of the barium titanate.

According to the liquid ejecting head of the fourth embodiment, althoughthe piezoelectric layer contains the predetermined proportions ofbismuth sodium titanate and barium titanate, the piezoelectric layer canhave a low leakage current and a good piezoelectricity.

Fifth Embodiment

In any one of the first to third embodiments, the piezoelectric layermay further contain bismuth potassium titanate.

According to the liquid ejecting head of the fifth embodiment, althoughthe piezoelectric layer further contains bismuth potassium titanate, thepiezoelectric layer can have a low leakage current and a goodpiezoelectricity.

Sixth Embodiment

In the fifth embodiment, the piezoelectric layer may contain less than100 mol % and 67 mol % or more of the bismuth sodium titanate, more than0 mol % and 30 mol % or less of the bismuth potassium titanate, and morethan 0 mol % and 3 mol % or less of the barium titanate.

According to the liquid ejecting head of the sixth embodiment, althoughthe piezoelectric layer contains the predetermined proportions ofbismuth sodium titanate, bismuth potassium titanate, and bariumtitanate, the piezoelectric layer can have a low leakage current and agood piezoelectricity.

Seventh Embodiment

A liquid ejecting apparatus according to a second aspect of theinvention includes the liquid ejecting head according to any one of thefirst to sixth embodiments.

Although the liquid ejecting apparatus of the seventh embodimentincludes a piezoelectric layer containing bismuth sodium titanate havinga low environmental load, the piezoelectric layer can have a low leakagecurrent and a good piezoelectricity.

Eighth Embodiment

A piezoelectric element according to a third aspect of the inventionincludes a piezoelectric layer formed by a thin-film method; and anelectrode that applies a voltage to the piezoelectric layer, wherein thepiezoelectric layer is composed of a solid solution containing bismuthsodium titanate and 0.2 mol % or more and 8.0 mol % or less of copper.

Although the piezoelectric element in the eighth embodiment includes apiezoelectric layer containing bismuth sodium titanate having a lowenvironmental load, the piezoelectric layer can have a low leakagecurrent and a good piezoelectricity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic sectional view of a piezoelectric element 100(piezoelectric actuator 102) according to an embodiment.

FIG. 2 is a schematic sectional view of a liquid ejecting head 600according to an embodiment.

FIG. 3 is an exploded perspective view illustrating a liquid ejectinghead 600 according to an embodiment.

FIG. 4 is a schematic perspective view illustrating a liquid ejectingapparatus 700 according to an embodiment.

FIG. 5 is a hysteresis loop of a piezoelectric element in Comparativeexample 1.

FIG. 6 is a hysteresis loop of a piezoelectric element in Example 1.

FIG. 7 is a hysteresis loop of a piezoelectric element in Example 3.

FIG. 8 is a hysteresis loop of a piezoelectric element in Example 5.

FIG. 9 is a hysteresis loop of a piezoelectric element in Comparativeexample 3.

FIG. 10 is a hysteresis loop of a piezoelectric element in Example 6.

FIG. 11 is a hysteresis loop of a piezoelectric element in Comparativeexample 4.

FIG. 12 is a hysteresis loop of a piezoelectric element in Example 7.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be describedwith reference to the drawings. Note that these embodiments describedbelow are mere examples of the invention. Accordingly, the invention isnot restricted to these embodiments and encompasses variousmodifications made without departing from the spirit and scope of theinvention. Note that the invention does not necessarily require all thefeatures described in the embodiments below.

1. Piezoelectric Element and Piezoelectric Actuator

FIG. 1 is a schematic sectional view of a piezoelectric element 100according to an embodiment of the invention.

The piezoelectric element 100 according to the embodiment includes afirst conductive layer 10, a second conductive layer 20, and apiezoelectric layer 30.

1.1. First Conductive Layer

The first conductive layer 10 is formed on, for example, a substrate 1.The substrate 1 may be, for example, a flat plate composed of anelectrical conductor, a semiconductor, or an electrical insulator. Thesubstrate 1 may have a structure constituted by a single layer or astack of a plurality of layers. As long as the substrate 1 has a topsurface that is flat, the internal structure thereof is not restricted.For example, the substrate 1 may have internal spaces. In the case wherepressure chambers and the like are formed under the substrate 1 as in aliquid ejecting head described below, the substrate 1 and such aplurality of components formed under the substrate 1 may be collectivelyregarded as the substrate 1.

The substrate 1 may have flexibility and serve as a vibration plate thatcan be deformed (bent) by the action of the piezoelectric layer 30. Inthis case, the piezoelectric element 100 functions as a piezoelectricactuator 102 including the vibration plate, the first conductive layer10, the piezoelectric layer 30, and the second conductive layer 20.Herein, when the substrate 1 has flexibility as described above, thesubstrate 1 can be bent. When the substrate 1 serves as a vibrationplate and the piezoelectric actuator 102 is used as a liquid ejectinghead, the degree to which the substrate 1 is bent will suffice that thevolume of the pressure chambers can be changed by substantially the samevalue as the volume of liquid to be ejected.

When the substrate 1 serves as a vibration plate, examples of a materialfor forming the substrate 1 include inorganic oxides such as zirconiumoxide (ZrO₂), silicon nitride, and silicon oxide; and alloys such asstainless steel. Of these, zirconium oxide is particularly preferred asthe material of the substrate 1 serving as a vibration plate in terms ofchemical stability and stiffness. The substrate 1 may have a structurein which layers composed of two or more of the listed materials arestacked.

In the embodiment, the case where the substrate 1 serves as a vibrationplate and is composed of zirconium oxide will be described as anexample. Accordingly, the piezoelectric element 100 is substantially thesame as the piezoelectric actuator 102 including a vibration plate thathas flexibility and can be deformed (bent) by the action of thepiezoelectric layer 30. In the following description, the piezoelectricelement 100 and the piezoelectric actuator 102 are interchangeable.

The shape of the first conductive layer 10 is not restricted as long asthe first conductive layer 10 can face the second conductive layer 20.However, since the piezoelectric layer 30 is formed so as to have theshape of a thin film in the embodiment, the first conductive layer 10 ispreferably formed so as to have the shape of a layer or a thin film. Thefirst conductive layer 10 may have a thickness of, for example, 50 nm ormore and 300 nm or less. The planar shape of the first conductive layer10 is also not restricted as long as the piezoelectric layer 30 can bedisposed between the first conductive layer 10 and the second conductivelayer 20 that face each other. The planar shape of the first conductivelayer 10 may be, for example, a rectangle, a circle, or the like.

A function of the first conductive layer 10 is to serve as an electrode(for example, a lower electrode formed under the piezoelectric layer 30)that applies a voltage to the piezoelectric layer 30, together with thesecond conductive layer 20 serving as another electrode. The firstconductive layer 10 may have a function of controlling crystalorientation during crystallization of the piezoelectric layer 30.

Examples of a material for forming the first conductive layer 10 includevarious metals such as nickel, iridium, and platinum; conductive oxidesof such metals (for example, iridium oxide); strontium-rutheniumcomposite oxides (SrRuO_(x): SRO); and lanthanum-nickel composite oxides(LaNiO_(x): LNO). The first conductive layer 10 may have a structureconstituted by a single layer composed of such a material or a pluralityof layers that are composed of two or more of the listed materials andare stacked.

1.2. Second Conductive Layer

The second conductive layer 20 is disposed so as to face the firstconductive layer 10. Specifically, the entirety of the second conductivelayer 20 may face the first conductive layer 10; alternatively, aportion of the second conductive layer 20 may face the first conductivelayer 10. The shape of the second conductive layer 20 is not restrictedas long as the second conductive layer 20 can face the first conductivelayer 10. However, since the piezoelectric layer 30 is formed so as tohave the shape of a thin film in the embodiment, the second conductivelayer 20 is preferably formed so as to have the shape of a layer or athin film. The second conductive layer 20 may have a thickness of, forexample, 50 nm or more and 300 nm or less. The planar shape of thesecond conductive layer 20 is also not restricted as long as thepiezoelectric layer 30 can be disposed between the second conductivelayer 20 and the first conductive layer 10 that face each other. Theplanar shape of the second conductive layer 20 may be, for example, arectangle, a circle, or the like.

A function of the second conductive layer 20 is to serve as an electrode(for example, an upper electrode formed on the piezoelectric layer 30)that applies a voltage to the piezoelectric layer 30, together with thefirst conductive layer 10 serving as another electrode. The secondconductive layer 20 may have a function of controlling crystalorientation during crystallization of the piezoelectric layer 30. Thesecond conductive layer 20 may be formed of a material/materials as inthe first conductive layer 10.

FIG. 1 illustrates an example in which the first conductive layer 10 isformed so as to have a larger planar area than the second conductivelayer 20. Alternatively, the second conductive layer 20 may be formed soas to have a larger planar area than the first conductive layer 10. Inthis case, the second conductive layer 20 may be formed so as to coverthe side surfaces of the piezoelectric layer 30 and the secondconductive layer 20 can also function as a protective layer thatprotects the piezoelectric layer 30 from moisture, hydrogen, or thelike.

1.3. Piezoelectric Layer

The piezoelectric layer 30 is disposed between the first conductivelayer 10 and the second conductive layer 20. The piezoelectric layer 30may be in contact with at least one of the first conductive layer 10 andthe second conductive layer 20. In the example illustrated in FIG. 1,the piezoelectric layer 30 is disposed so as to be in contact with thefirst conductive layer 10 and the second conductive layer 20.

The piezoelectric layer 30 is formed by a thin-film method. Herein, theterm “thin-film method” refers to at least one method among a sputteringmethod, a deposition method, a metal-organic chemical vapor deposition(MOCVD) method, a metal-organic decomposition (MOD) method, a pulsedlaser deposition (PLD) (laser ablation) method, a mist film-formationmethod, and a sol-gel method. Accordingly, the piezoelectric layer 30 inthe embodiment is not formed in the form of a bulk. That is, thepiezoelectric layer 30 is not formed by, for example, forming a bulk andthen reducing the thickness of the bulk by polishing or the like to turnthe bulk into a thin film.

The thickness of the piezoelectric layer 30 is not restricted as long asthe piezoelectric layer 30 is formed by a thin-film method and may be,for example, 100 nm or more and 3,000 nm or less. Consider the caseswhere the piezoelectric layer 30 having a large thickness is formed by athin-film method. For example, when a method of depositing a materialsuch as a sputtering method, a deposition method, or an MOCVD method isemployed, the piezoelectric layer 30 having a large thickness can beformed by increasing the time over which the deposition is performed.Alternatively, for example, when a method in which coating and firingare performed such as an MOD method or a sol-gel method is employed, thepiezoelectric layer 30 having a large thickness can be formed byrepeating such a method to stack the resultant layers. In such a casewhere layers are stacked, different thin-film methods may be employedfor forming the layers. When the piezoelectric layer 30 has a thicknessthat is not within the above-described range, there may be cases wherethe withstand voltage of the piezoelectric layer 30 is insufficient orsufficient deformation (electromechanical transduction) of thepiezoelectric layer 30 is not achieved.

The piezoelectric layer 30 in the embodiment is composed of a solidsolution containing bismuth sodium titanate and 0.2 mol % or more and8.0 mol % or less of copper. Bismuth sodium titanate, which can berepresented by, for example, (Bi_(0.5), Na_(0.5))TiO₃ (hereafter,sometimes abbreviated as “BNT”), is classified as a perovskite oxide,that is, a composite oxide represented by a general formula ABO₃ wherebismuth atoms and sodium atoms occupy the A sites and titanium atomsoccupy the B sites. BNT can have a perovskite crystalline structure as aresult of crystallization and can exhibit piezoelectricity in the formof a bulk. However, while a bulk composed of BNT only can exhibit a goodhysteresis loop, a thin film composed of BNT only has high leakagecurrent and cannot exhibit a good hysteresis loop. The inventors of theinvention consider that this is probably caused by the following reason.As for the BNT bulk, a piezoelectric layer is fired at 1,000° C. or moreand then an electrode is formed at a low temperature. In contrast, asfor the BNT thin film, a piezoelectric layer is formed at a hightemperature on a previously formed electrode and hence a good interfaceis not formed between the piezoelectric layer and the electrode. Thepiezoelectric layer 30 in the embodiment is formed so as to containbismuth sodium titanate and a predetermined amount of copper and henceeven when the piezoelectric layer 30 is formed by a thin-film method,the piezoelectric layer 30 has a low leakage current and can exhibit agood hysteresis loop. Thus, in the embodiment, a good interface isprobably formed between the piezoelectric layer 30 and the firstconductive layer 10. Accordingly, the piezoelectric layer 30 can bedeformed by the application of an electric field with the firstconductive layer 10 and the second conductive layer 20. As a result ofthe deformation, for example, the substrate 1 can be bent or vibrated.Thus, the piezoelectric actuator 102 can be provided.

The piezoelectric layer 30 can be made to contain bismuth sodiumtitanate and 0.2 mol % or more and 4.0 mol % or less of copper. In thispiezoelectric layer 30, leakage current can be reduced. Furthermore, thepiezoelectric layer 30 can be made to contain bismuth sodium titanateand 0.5 mol % or more and 4.0 mol % or less of copper. In thispiezoelectric layer 30, leakage current can be further reduced.

When the piezoelectric layer 30 in the embodiment is composed of a solidsolution mainly containing bismuth sodium titanate, for example, thepiezoelectric layer 30 may have a mixed crystal configuration containingless than 100 mol % and 50 mol % or more of bismuth sodium titanate andmore than 0 mol % and less than 50 mol % of another piezoelectricmaterial(s). Such another piezoelectric material(s) may be a perovskiteoxide(s) and may be at least one selected from the lead-free compoundgroup consisting of barium titanate, bismuth potassium titanate, sodiumniobate, potassium niobate, lithium niobate, bismuth ferrite, bismuthchromate, bismuth cobaltate, and bismuth aluminate. For example, thepiezoelectric layer 30 can be made to contain less than 100 mol % and 85mol % or more of bismuth sodium titanate and more than 0 mol % and 15mol % or less of barium titanate. Alternatively, for example, thepiezoelectric layer 30 can be made to contain less than 100 mol % and 67mol % or more of bismuth sodium titanate, more than 0 mol % and 30 mol %or less of bismuth potassium titanate, and more than 0 mol % and 3 mol %or less of barium titanate. Barium titanate can be represented by, forexample, BaTiO₃ (hereafter, sometimes abbreviated as “BT”). Bismuthpotassium titanate can be represented by, for example, (Bi_(0.5),K_(0.5))TiO₃ (hereafter, sometimes abbreviated as “BKT”). When BNT, BT,BKT, or the like has a stoichiometric composition, the composition ratio(hereafter, referred to as A/B) of the molar amount of an element(s)occupying the A sites to the molar amount of an element(s) occupying theB sites in ABO₃ is 1. However, BNT, BT, BKT, or the like may have anon-stoichiometric composition. The amount (mol %) of copper added tothe piezoelectric layer 30 in the embodiment is based on 100 mol % ofbismuth sodium titanate or 100 mol % of a mixed-crystal perovskiteoxide(s).

1.4. Advantages and the Like

The piezoelectric element 100 (piezoelectric actuator 102) according tothe embodiment includes the piezoelectric layer 30 and hence at leasthas low leakage current and exhibits a good hysteresis loop. Thehysteresis loop of the piezoelectric layer 30 is obtained by subjectingthe piezoelectric layer 30 to a P-E measurement and can be used as acriterion with which the piezoelectricity of the piezoelectric layer 30is evaluated. Specifically, the piezoelectric layer 30 exhibiting a goodhysteresis loop can be evaluated as having a good piezoelectricity. Thepiezoelectric layer 30 according to the embodiment is composed of alead-free compound(s) and hence can have a low environmental load andcan also have a good piezoelectricity.

The piezoelectric element 100 according to the embodiment can be usedfor a wide range of applications. The piezoelectric actuator 102 isapplicable to, for example, a liquid ejecting head, a liquid ejectingapparatus such as an ink jet printer, or the like. The piezoelectricelement 100 is suitably applicable to a sensor such as a gyro sensor oran acceleration sensor, a timing device such as a tuning fork vibrator,or an ultrasonic device such as an ultrasonic motor.

2. Production Method of Piezoelectric Element

The piezoelectric element 100 according to the embodiment can beproduced in, for example, the following manner.

The substrate 1 is prepared. Then, the first conductive layer 10 isformed on the substrate 1. The first conductive layer 10 may be formedby, for example, a sputtering method, a plating method, a vacuumdeposition method, or the like. If necessary, the first conductive layer10 may be patterned.

Then, the piezoelectric layer 30 is formed on the first conductive layer10. As described above, the piezoelectric layer 30 can be formed by, forexample, at least one method selected from a sputtering method, adeposition method, a metal-organic chemical vapor deposition (MOCVD)method, a metal-organic decomposition (MOD) method, a pulsed laserdeposition (PLD) (laser ablation) method, a mist film-formation method,and a sol-gel method; or a plurality of methods in combination selectedfrom these methods. The piezoelectric layer 30 can be crystallized, forexample, at a temperature of 550° C. or more and 800° C. or less and inan oxygen atmosphere. The heat-treatment temperature for thecrystallization of the piezoelectric layer 30 may be, for example, 550°C. or more and 850° C. or less, or may be 600° C. or more and 750° C. orless. Note that the crystallization may be performed after thepiezoelectric layer 30 is patterned. If necessary, such a step may berepeated such that the piezoelectric layer 30 having a desired thicknessis provided.

Then, the second conductive layer 20 is formed on the piezoelectriclayer 30. The second conductive layer 20 may be formed by, for example,a sputtering method, a plating method, a vacuum deposition method, orthe like. Subsequently, the second conductive layer 20 and thepiezoelectric layer 30 are patterned so as to have a desired shape.Thus, the piezoelectric element is formed. Note that, if necessary, thesecond conductive layer 20 and the piezoelectric layer 30 may besimultaneously patterned. The piezoelectric element 100 according to theembodiment can be produced through such steps having been described asan example.

3. Liquid Ejecting Head

Hereinafter, as an example of the application of a piezoelectric element(piezoelectric actuator) according to the embodiment, a liquid ejectinghead 600 including such a piezoelectric element (piezoelectric actuator)will be described with reference to drawings. FIG. 2 is a schematicsectional view illustrating a main portion of the liquid ejecting head600. FIG. 3 is an exploded perspective view of the liquid ejecting head600 illustrated upside down.

The liquid ejecting head 600 can include the above-describedpiezoelectric element (piezoelectric actuator). Hereinafter, the liquidejecting head 600 in which the piezoelectric element 100 is formed onthe substrate 1 (structure including a vibration plate 1 a in an upperportion thereof) and the piezoelectric element 100 and the vibrationplate 1 a constitute the piezoelectric actuator 102, will be describedas an example.

As illustrated in FIGS. 2 and 3, the liquid ejecting head 600 includes anozzle plate 610 including nozzle openings 612, a pressure chambersubstrate 620 for forming pressure chambers 622, and the piezoelectricelement 100. As illustrated in FIG. 3, the liquid ejecting head 600 mayfurther include a casing 630. Note that the piezoelectric element 100 issimply illustrated in FIG. 3.

As illustrated in FIGS. 2 and 3, the nozzle plate 610 includes thenozzle openings 612. Ink can be ejected through the nozzle openings 612.For example, a large number of the nozzle openings 612 are arranged in aline on the nozzle plate 610. The nozzle plate 610 may be formed of amaterial such as silicon or stainless steel (SUS).

The pressure chamber substrate 620 is disposed on the nozzle plate 610(in FIG. 3, under the nozzle plate 610). The pressure chamber substrate620 may be formed of a material such as silicon. As illustrated in FIG.3, the pressure chamber substrate 620 sections the space between thenozzle plate 610 and the vibration plate 1 a into a reservoir (liquidstorage section) 624, supply ports 626 in communication with thereservoir 624, and the pressure chambers 622 in communication with thesupply ports 626. In the example, the reservoir 624, the supply ports626, and the pressure chambers 622 are described as different portions.However, all these portions are liquid channels and such channels may befreely designed. For example, in the example illustrated in FIG. 3, thesupply ports 626 correspond to narrowed portions of the liquid channels.However, the supply ports 626 may be freely formed depending on a designand are not necessarily indispensable portions. The reservoir 624, thesupply ports 626, and the pressure chambers 622 are delimited by thenozzle plate 610, the pressure chamber substrate 620, and the vibrationplate 1 a. The reservoir 624 is configured to temporarily store inktherein, the ink being fed from the outside (for example, an inkcartridge) through a through hole 628 provided in the vibration plate 1a. The ink in the reservoir 624 can be fed through the supply ports 626to the pressure chambers 622. The volume of the pressure chambers 622 ischanged by deformation of the vibration plate 1 a. The pressure chambers622 are in communication with the nozzle openings 612. As a result of achange in the volume of the pressure chambers 622, ink or the like isejected through the nozzle openings 612.

The piezoelectric element 100 is disposed on the pressure chambersubstrate 620 (in FIG. 3, under the pressure chamber substrate 620). Thepiezoelectric element 100 is electrically connected to a piezoelectricelement driving circuit (not shown) and can be made to operate (vibrateor deform) on the basis of signals fed from the piezoelectric elementdriving circuit. The vibration plate 1 a can be deformed by the actionof the piezoelectric layer 30 to thereby appropriately change theinternal pressure of the pressure chambers 622.

As illustrated in FIG. 3, the casing 630 can contain the nozzle plate610, the pressure chamber substrate 620, and the piezoelectric element100. The casing 630 may be formed of a material such as a resin or ametal.

The liquid ejecting head 600 includes the above-described piezoelectricelement 100, which at least has a high withstand voltage. Accordingly,the liquid ejecting head 600 has a high withstand voltage, can beoperated under a high voltage, and has a high capability of ejectingliquid or the like, compared with existing liquid ejecting heads.

Note that the case where the liquid ejecting head 600 is an ink jetrecording head was described above. However, a liquid ejecting headaccording to the embodiment can also be used as, for example, a colorantejecting head used for producing color filters of liquid crystaldisplays or the like; an electrode material ejecting head used forforming electrodes of organic EL displays, field emission displays(FEDs), or the like; or a bioorganic material ejecting head used forproducing biochips.

4. Liquid Ejecting Apparatus

Hereinafter, a liquid ejecting apparatus according to an embodiment ofthe invention will be described with reference to a drawing. The liquidejecting apparatus includes the above-described liquid ejecting head. Inthe following description, a case where the liquid ejecting apparatus isan ink jet printer including the above-described liquid ejecting headwill be described. FIG. 4 is a schematic perspective view illustrating aliquid ejecting apparatus 700 according to the embodiment.

As illustrated in FIG. 4, the liquid ejecting apparatus 700 includes ahead unit 730, a driving section 710, and a control section 760. Theliquid ejecting apparatus 700 may further include an apparatus body 720,a paper sheet supply section 750, a tray 721 on which recording papersheets P are placed, an ejection opening 722 for ejecting recordingpaper sheets P, and an operation panel 770 disposed on the top surfaceof the apparatus body 720.

The head unit 730 includes an ink jet recording head (hereafter, may besimply referred to as “head”) constituted by the above-described liquidejecting head 600. The head unit 730 further includes an ink cartridge731 for supplying ink to the head and a carrying section (carriage) 732on which the head and the ink cartridge 731 are mounted.

The driving section 710 can reciprocate the head unit 730. The drivingsection 710 includes a carriage motor 741 serving as a driving source ofthe head unit 730, and a reciprocating mechanism 742 configured toreciprocate the head unit 730 by the rotation of the carriage motor 741.

The reciprocating mechanism 742 includes a carriage guide shaft 744 bothends of which are supported by a frame (not shown), and a timing belt743 extending in parallel with the carriage guide shaft 744. Thecarriage guide shaft 744 supports the carriage 732 such that thecarriage 732 can be freely reciprocated. The carriage 732 is fixed to aportion of the timing belt 743. When the timing belt 743 is run by theaction of the carriage motor 741, the head unit 730 reciprocates whilebeing guided by the carriage guide shaft 744. During this reciprocation,ink is appropriately ejected from the head to perform printing on therecording paper sheet P.

Note that the embodiment describes an example of the liquid ejectingapparatus in which printing is performed while both the liquid ejectinghead 600 and the recording paper sheets P are moved. However, it willsuffice that a liquid ejecting apparatus according to the invention hasa mechanism in which printing is performed on the recording paper sheetsP while the liquid ejecting head 600 and the recording paper sheets Pare moved relative to each other. The embodiment describes an example inwhich printing is performed on the recording paper sheets P. However,recording media on which printing can be performed with a liquidejecting apparatus according to the invention are not restricted topaper and may encompass various media such as cloth, film, metal, andthe like. The configuration of the liquid ejecting apparatus can bemodified in accordance with such media.

The control section 760 can control the head unit 730, the drivingsection 710, and the paper sheet supply section 750.

The paper sheet supply section 750 can transport the recording papersheet P from the tray 721 to the head unit 730 side. The paper sheetsupply section 750 includes a paper sheet supply motor 751 serving as adriving source of the paper sheet supply section 750 and paper sheetsupply rollers 752 rotated by the action of the paper sheet supply motor751. The paper sheet supply rollers 752 include a driven roller 752 aand a driving roller 752 b that vertically face each other with atransporting path of the recording paper sheets P therebetween. Thedriving roller 752 b is connected to the paper sheet supply motor 751.When the paper sheet supply section 750 is driven by the control section760, the recording paper sheet P is transported so as to be passed underthe head unit 730.

The head unit 730, the driving section 710, the control section 760, andthe paper sheet supply section 750 are disposed inside the apparatusbody 720.

The liquid ejecting apparatus 700 includes the liquid ejecting head 600,which has a high withstand voltage. Accordingly, the liquid ejectingapparatus 700 has a high capability of ejecting liquid.

Note that the liquid ejecting apparatus 700 described above as anexample includes a single liquid ejecting head 600 and is configured toperform printing on recording media with the liquid ejecting head 600.Alternatively, the liquid ejecting apparatus may include a plurality ofliquid ejecting heads. When the liquid ejecting apparatus includes aplurality of liquid ejecting heads, the plurality of liquid ejectingheads may be independently operated in the above-described manner, orthe plurality of liquid ejecting heads may be joined together and usedas a single head assembly. An example of such a head assembly includes alinear head in which the nozzle openings of a plurality of heads arearranged at a uniform pitch.

As an example of a liquid ejecting apparatus according to the invention,the liquid ejecting apparatus 700 serving as an ink jet printer has beendescribed. However, a liquid ejecting apparatus according to theinvention can also be used as an industrial liquid ejecting apparatus.In this case, liquid (liquid material) ejected by such an apparatus maybe, for example, a functional material that is adjusted to have anappropriate viscosity with a solvent or a dispersion medium. A liquidejecting apparatus according to the invention can be suitably used as,in addition to an image recording apparatus such as a printer describedabove as an example, a colorant ejecting apparatus used for producingcolor filters of liquid crystal displays or the like; a liquid materialejecting apparatus used for forming electrodes or color filters oforganic EL displays, field emission displays (FEDs), electrophoreticdisplays, or the like; or a bioorganic material ejecting apparatus usedfor producing biochips.

5. Examples and Comparative Examples

Hereinafter, the invention will be specifically described with referenceto Examples and Comparative examples. However, the invention is notrestricted by the following Examples.

5.1. Fabrication of Piezoelectric Elements

Piezoelectric elements in Examples 1 to 7 and Comparative examples 1 to4 were fabricated in the following manner.

A substrate was produced by the following steps. A silicon dioxide filmserving as an insulation film was formed on a single crystal siliconsubstrate by thermal oxidation. A titanium (Ti) film was formed on thesilicon dioxide film by a RF magnetron sputtering method so as to have athickness of 40 nm and was thermally oxidized to thereby form a titaniumoxide film. A platinum (Pt) film was further formed on the titaniumoxide film by a RF magnetron sputtering method so as to have a thicknessof 100 nm. Thus, a lower electrode oriented in the (111) plane wasformed. This lower electrode corresponds to the first conductive layer10 in the above-described embodiment.

The piezoelectric layers 30 in Examples and Comparative examples weresubsequently formed by a chemical solution method. Material solutionsused in the chemical solution method were each prepared by mixing ametal alkoxide or an organic acid metal salt with a solvent (n-butanol).The material solutions were prepared so as to have metal compositionssummarized in Tables 1 to 3 below. Tables 1 to 3 show the amounts ofmaterials mixed, that is, mixing amounts (mol %). Each thin film wasformed in the following manner. Such a material solution was spin-coatedon the substrate on which the lower electrode had been formed, at 500rpm for 10 seconds and then at 2,500 rpm for 30 seconds. The substratewas then placed on a hot plate at 150° C. and dried for 3 minutes. Thesubstrate was then placed on a hot plate at 400° C. and calcined for 5minutes. Such a step from the spin-coating to the calcination wasrepeated six times. Then, the substrate was annealed at 750° C. for 2minutes in an oxygen atmosphere to provide the thin-film piezoelectriclayer 30 by firing.

Lastly, a platinum (Pt) layer having a film thickness of 100 nm wasformed by a DC sputtering method through a metal mask having openingshaving a diameter of 500 μm, on the substrate on which the lowerelectrode and the piezoelectric layer 30 had been formed. This platinum(Pt) layer is an upper electrode and corresponds to the secondconductive layer 20 in the above-described embodiment.

In Comparative examples 1 and 2 and Examples 1 to 5, 0 mol % or more and16 mol % or less of copper (Cu) was added with respect to 100 mol % ofbismuth sodium titanate (Bi_(0.5), Na_(0.5))TiO₃.

In Comparative example 3 and Example 6, 0 mol % and 1 mol % of copper(Cu) were added with respect to 85 mol % of bismuth sodium titanate((Bi_(0.5), Na_(0.5))TiO₃) and 15 mol % of barium titanate (BaTiO₃).

In Comparative example 4 and Example 7, 0 mol % and 1 mol % of copper(Cu) were added with respect to 67 mol % of bismuth sodium titanate((Bi_(0.5), Na_(0.5))TiO₃), 30 mol % of bismuth potassium titanate((Bi_(0.5), K_(0.5))TiO₃), and 3 mol % of barium titanate (BaTiO₃).

5.2. Evaluation of Piezoelectric Elements

5.2.1. Evaluation of Leakage Current

The piezoelectric elements in Examples and Comparative examples weremeasured in terms of leakage current value with 4140B manufactured byHewlett-Packard Company under evaluation conditions (delay time: 0.5sec, hold time: 0.5 sec, applied electric field: 200 kV/cm, 300 kV/cm,400 kV/cm, and 600 kV/cm). The piezoelectric elements were evaluated onthe basis of the measured leakage current values. The measurementresults are shown in Tables 1 to 3 below. Cases in Table 1 where a shortcircuit occurred and leakage current values were not measured arerepresented by “Short”.

TABLE 1 Leakage current value [A/cm²] Leakage current value [A/cm²]under applied electric field of under applied electric field of(Bi_(0.5), Na_(0.5))TiO₃ (Bi_(0.5), K_(0.5))TiO₃ BaTiO₃ Cu 200 kV/cm 400kV/cm Unit mol % mol % mol % mol % Positive Negative Positive NegativeComparative 100 0 0 0 0.042598726 0.003042038 0.312356688 0.082038217example 1 Example 1 100 0 0 0.2 0.000365860 0.000781769 0.2114649680.021044586 Example 2 100 0 0 0.5 0.000001676 0.000119745 0.0047771960.003880835 Example 3 100 0 0 1 0.000025427 0.000008764 0.0005839490.000599745 Example 4 100 0 0 4 0.000024090 0.000345478 0.0001268150.001125544 Example 5 100 0 0 8 0.009115924 0.005383258 0.470318471Short Comparative 100 0 0 16 Short Short Short Short example 2

TABLE 2 Leakage current value [A/cm²] Leakage current value [A/cm²]under applied electric field of under applied electric field of(Bi_(0.5), Na_(0.5))TiO₃ (Bi_(0.5), K_(0.5))TiO₃ BaTiO₃ Cu 300 kV/cm 600kV/cm Unit mol % mol % mol % mol % Positive Negative Positive NegativeComparative 85 0 15 0 0.000029488 0.000186912 0.002235809 0.003004846example 3 Example 6 85 0 15 1 0.000001304 0.000030965 0.0000443600.000162975

TABLE 3 Leakage current value [A/cm²] Leakage current value [A/cm²]under applied electric field of under applied electric field of(Bi_(0.5), Na_(0.5))TiO₃ (Bi_(0.5), K_(0.5))TiO₃ BaTiO₃ Cu 300 kV/cm 600kV/cm Unit mol % mol % mol % mol % Positive Negative Positive NegativeComparative 67 30 3 0 0.000008607 0.000112554 0.000244971 0.003677117example 4 Example 7 67 30 3 1 0.000000346 0.000000474 0.0000014770.0000020935.2.2. Evaluation of Hysteresis

The piezoelectric elements in Examples and Comparative examples weremeasured in terms of hysteresis with FCE-1A manufactured by TOYOCorporation under measurement conditions (measurement temperature: roomtemperature, frequency: 1 kHz, waveform: triangular wave, appliedelectric field: 400 kV/cm and 630 kV/cm) to provide hysteresis loops.The piezoelectric elements were evaluated on the basis of the shape ofthe hysteresis loops. The samples of Examples and Comparative examplesused in this evaluation were the same as those in the evaluation ofleakage current. FIG. 5 is a hysteresis loop of the piezoelectricelement in Comparative example 1. FIG. 6 is a hysteresis loop of thepiezoelectric element in Example 1. FIG. 7 is a hysteresis loop of thepiezoelectric element in Example 3. FIG. 8 is a hysteresis loop of thepiezoelectric element in Example 5. FIG. 9 is a hysteresis loop of thepiezoelectric element in Comparative example 3. FIG. 10 is a hysteresisloop of the piezoelectric element in Example 6. FIG. 11 is a hysteresisloop of the piezoelectric element in Comparative example 4. FIG. 12 is ahysteresis loop of the piezoelectric element in Example 7.

5.3. Evaluation Results

The leakage current values under the applied electric field of 200 kV/cmin Table 1 are compared with each other. Compared with Comparativeexample 1 in which copper was not added, Examples 1 to 5 in which 0.2mol % or more and 8 mol % or less of copper were added have low leakagecurrent values. In Comparative example 2, a short circuit occurred inboth the positive side and the negative side. The leakage current valuesunder the applied electric field of 400 kV/cm in Table 1 are comparedwith each other. Compared with Comparative example 1 in which copper wasnot added, Examples 1 to 4 in which 0.2 mol % or more and 4 mol % orless of copper were added have low leakage current values. A shortcircuit occurred in the negative side of Example 5 and Comparativeexample 2. Thus, it has been demonstrated that addition of apredetermined amount of copper results in a decrease in a leakagecurrent value though the decrease varies in accordance with the appliedelectric field.

The leakage current values under the applied electric field of 300 kV/cmin Table 2 are compared with each other. Compared with Comparativeexample 3 in which copper was not added, Example 6 in which 1 mol % ofcopper was added has low leakage current values. The leakage currentvalues under the applied electric field of 600 kV/cm in Table 2 arecompared with each other. Compared with Comparative example 3 in whichcopper was not added, Example 6 in which 1 mol % of copper was added haslow leakage current values. Thus, it has been demonstrated that additionof 1 mol % of copper results in a decrease in a leakage current valueeven in the case where a piezoelectric element contains 15 mol % ofbarium titanate as well as bismuth sodium titanate.

The leakage current values under the applied electric field of 300 kV/cmin Table 3 are compared with each other. Compared with Comparativeexample 4 in which copper was not added, Example 7 in which 1 mol % ofcopper was added has low leakage current values. The leakage currentvalues under the applied electric field of 600 kV/cm in Table 3 arecompared with each other. Compared with Comparative example 4 in whichcopper was not added, Example 7 in which 1 mol % of copper was added haslow leakage current values. Thus, it has been demonstrated that additionof 1 mol % of copper results in a decrease in a leakage current valueeven in the case where a piezoelectric element contains bismuthpotassium titanate as well as bismuth sodium titanate and bariumtitanate.

Referring to FIGS. 5 to 8, compared with the hysteresis loop ofComparative example 1 being roundish due to influence of leakagecurrent, the hysteresis loops of Examples 1, 3, and 5 in which thepredetermined amounts of copper were added have good sharp shapes andhence a good piezoelectricity is exhibited.

Referring to FIGS. 9 and 10, the hysteresis loop of Example 6 in which 1mol % of copper was added has a better shape than that of Comparativeexample 3. Thus, it has been demonstrated that, even in the case where apiezoelectric layer contains 15 mol % of barium titanate, addition of 1mol % of copper results in a good piezoelectricity.

Referring to FIGS. 11 and 12, the hysteresis loop of Example 7 in which1 mol % of copper was added has a better shape than that of Comparativeexample 4. Thus, it has been demonstrated that, even in the case where apiezoelectric layer contains 3 mol % of barium titanate and 30 mol % ofbismuth potassium titanate, addition of 1 mol % of copper results in agood piezoelectricity.

As has been described above, it has been demonstrated that piezoelectricelements according to the invention have a low environmental load and agood piezoelectricity.

Two or more embodiments freely selected from the above-describedembodiments and modified embodiments can be appropriately combined. Insuch cases, the resultant embodiment can provide advantages of theoriginal embodiments or can synergistically provide advantages of theoriginal embodiments.

The invention is not restricted to the above-described embodiments andvarious modifications can be further made. For example, the inventionencompasses substantially the same configurations (for example, aconfiguration having the same function, method, and result or aconfiguration having the same object and advantageous effect) as theconfigurations described in the embodiments. In addition, the inventionencompasses configurations in which nonessential components are replacedin the configurations described in the embodiments. In addition, theinvention encompasses configurations that provide the same function andadvantageous effects or can achieve the same object as theconfigurations described in the embodiments. In addition, the inventionencompasses configurations in which the configurations described in theembodiments are combined with existing techniques.

What is claimed is:
 1. A piezoelectric element comprising: apiezoelectric layer; and an electrode which applies a voltage to thepiezoelectric layer, wherein the piezoelectric layer is composed of asolid solution containing bismuth sodium titanate and copper, andwherein when a leakage current of the piezoelectric element is measuredwith a delay time of 0.5 sec, a hold time of 0.5 sec and an appliedelectric field of 200 kV/cm, the leakage current value is 0.000001676 to0.009115924 A/cm2.
 2. The piezoelectric element according to claim 1,wherein the piezoelectric layer contains 0.2 mol % or more and 8.0 mol %or less of copper.
 3. The piezoelectric element according to claim 1,wherein the piezoelectric layer further contains barium titanate.
 4. Thepiezoelectric element according to claim 3, wherein the piezoelectriclayer contains less than 100 mol % and 85 mol % or more of the bismuthsodium titanate; and the piezoelectric layer contains more than 0 mol %and 15 mol % or less of the barium titanate.
 5. The piezoelectricelement according to claim 1, wherein the piezoelectric layer furthercontains bismuth potassium titanate.
 6. The piezoelectric elementaccording to claim 5, wherein the piezoelectric layer contains less than100 mol % and 67 mol % or more of the bismuth sodium titanate; thepiezoelectric layer contains more than 0 mol % and 30 mol % or less ofthe bismuth potassium titanate; and the piezoelectric layer containsmore than 0 mol % and 3 mol % or less of the barium titanate.
 7. Thepiezoelectric element according to claim 1, wherein the piezoelectriclayer is formed by a thin-film method.
 8. A liquid ejecting apparatuscomprising the piezoelectric element according to claim
 1. 9. A liquidejecting head comprising the piezoelectric element according to claim 1.10. An ultrasonic device comprising the piezoelectric element accordingto claim
 1. 11. A sensor comprising the piezoelectric element accordingto claim
 1. 12. A timing device comprising the piezoelectric elementaccording to claim 1.